Ball grid array (BGA) packages can provides an integrated circuit device with a package having a high density of terminals. FIG. 1A illustrates an example of a conventional BGA package 100 containing a semiconductor device 110 on an interconnect substrate 140. Device 110, which can be any sort of semiconductor device, generally has electrical contact pads that are electrically connected to contact pads or traces on interconnect substrate 140. FIG. 1A shows an example where wire bonds 120 electrically connect semiconductor device 110 to interconnect substrate 140, and an encapsulant 130 protects and insulates wire bonds 120. Alternatively, other electrical connection techniques such as flip-chip packaging techniques can provide the electrical connections to interconnect substrate 140. Interconnect substrate 140 is generally made of an insulating containing the conductive traces (not shown) that provide electrical signals paths. The contact pads or terminals of device 110 are connected to the conductive traces in and on an interconnect substrate 140 and through the conductive traces are connected to external terminals 150.
External terminals 150 can be arranged in an array commonly referred to as a ball grid array (BGA) and are typically metal bumps such as solder balls. Solder in external terminals 150 can be reflowed to attach package 100 to a printed circuit board or other electrical system. A difficulty that can arise when connecting package 100 in an electrical system is non-uniformity of the elevation of terminals 150. In particular, the manufacturing process will generally create some terminals 150′ that are larger than average and some terminals 150″ that are smaller than average. The smaller terminals 150″ may not make good contact to an underlying printed circuit board or system during a reflow or other soldering process, resulting in less dependable connections.
Warping of the interconnect substrate can similarly make electrical connections less dependable. FIG. 1B illustrates a flip-chip package 102 containing device 110. In flip-chip package 102, metal bumps 122 on the contact pads of device 110 contact pads or traces on a interconnect substrate 142. An insulating fill material 132 between device 110 and interconnect substrate 142 can be used to improve the thermal or mechanical properties of package 102.
The manufacturing process for interconnect substrate 142 or the process of attaching interconnect substrate 142 to device 110 can cause warping of substrate 142. In particular, fill material 132 between device 110 and substrate 142, which varies in thickness or shape on interconnect substrate 142, can introduce stress that causes warping. Such warping is particularly common when substrate 142 is relatively thin (e.g., less than about 2 mm thick) for a low profile package. Regardless of the cause, the warping of substrate 142 can change the elevations of terminals 150, moving some of the external terminals 150′″ away from the flat surface of a printed circuit board to which package 102 attaches. The warping thus results in a non-planar array of terminals 150 and in less dependable electrical connections.
Methods for improving the planarity of ball grid arrays or other the external terminals of device packages can improve the quality of electrical connections formed when connecting the packages in a larger system.